1. Field of the Invention
The present invention relates to an image processing apparatus and a method for supporting imaging diagnosis of an eye, and particularly, to an image processing apparatus and a method using a tomographic image of an eye.
2. Description of the Related Art
In recent years, eyes are often inspected to provide early diagnosis of diseases that are ranked high in causing lifestyle-related diseases and blindness. Tomographic eye image pickup apparatus, such as those for Optical Coherence Tomography (OCT), can observe in three-dimensions, the state inside a retinal layer, and the apparatus are expected to be useful in providing a more accurate diagnosis of a disease.
FIG. 3 shows a schematic diagram of a topographic image of a macular area of a retina taken by OCT. OCT takes an image of an eye to acquire a volume image formed by a set of a plurality of two-dimensional tomographic images. In FIG. 3, T1 to Tn denote two-dimensional tomographic images (B scan images, hereinafter called “tomographic images”). In each tomographic image Tk, the horizontal direction of the tomographic image is defined as an X-axis direction, and the depth direction is defined as a Z-axis direction. The lines parallel to the Z axis of the tomographic image will be called A scan lines. In the tomographic image Tk, L1 denotes an inner limiting membrane, L2 denotes a boundary of a nerve fiber layer and a layer below (hereinafter called “nerve fiber layer boundary), L3 denotes a visual cell internal junction, and L4 denotes a retinal pigment epithelial boundary.
The state of the retinal layer is significantly meaningful in the imaging diagnosis using OCT. For example, in glaucoma, the nerve fiber layer between the inner limiting membrane L1 and the nerve fiber layer boundary L2 becomes thinner as the disease progresses. In age-related macular degeneration, a choroidal neovascular is generated at the lower part of the retinal pigment epithelial boundary L4. Therefore, the retinal pigment epithelial boundary L4 is deformed.
The retinal layer boundary needs to be detected first for quantitative and objective measurement of the change in the state of the retinal layer. Therefore, a technique for using an image analysis technique to detect the boundaries of the retinal layers is being developed. A technique for identifying the retinal layer boundary described in U.S. Pat. No. 6,293,674 focuses on a point that the luminance variations from the parts other than the retinal layer are large at the inner limiting membrane and the retinal pigment epithelial boundary. Two strong edges are detected in each A scan line. The edge with smaller Z coordinate values is set as the inner limiting membrane, and the edge with larger Z coordinate values is set as the retinal pigment epithelial boundary.
However, strong edges are just detected and associated in each A scan line in the retinal layer boundary detection described in U.S. Pat. No. 6,293,674. Therefore, if the retinal layer boundary is imaged so that part of the boundary extends above the two-dimensional tomographic image as shown in FIGS. 4A and 4B, there is a problem that the detection of the retinal layer boundary fails because two strong edges are associated with different boundaries. A false detection of the retinal layer boundary can be prevented if the A scan lines without the retinal layer boundary are detected in advance, and the retinal layer boundary is detected only by the A scan lines with the retinal layer boundary. However, it is difficult to identify the A scan lines without the retinal layer boundary without detecting the retinal layer boundary.